During the last decades environmental aspects such as reduction of fossil fuel consumption, reduction of exhaust emissions, increased energy efficiency etc. have been the main focus for the automotive industry. This is partly because of new, tougher legislation and industry commitments, but also due to an increasing demand and growing interest from the market. Except for optimization and development of the conventional combustion engine and the powertrain in regards of minimized friction, higher efficiency, more intelligent control systems, optimized combustion, optimized fuels, better aftertreatment systems etc., one of the most promising approaches in order to meet these prerequisites is increased electrification of the powertrain.
As of today, there are still some technological advances to be done in order to replace conventional vehicles with ICEs with electrical vehicles, e.g., the fully electrified vehicles of today generally have limited range capabilities and generally need substantial time to recharge their batteries. The predominating, partly electrified vehicles of today are HEVs, combining the conventional ICE with an EE, wherein the ICE may be partly or completely disabled during certain driving conditions. Disabling the ICE reduces the fuel consumption, but generally HEVs also need smaller ICEs, reducing the fuel consumption even more.
There are numerous configurations of HEVs, but conceptually they can generally be divided into two categories; serial hybrids and parallel hybrids. Serial hybrids generally have a generator connected to the ICE, and the generator provides energy to the EE, wherein the EE is used to drive the vehicle. In parallel hybrid vehicles both the ICE and the EE can drive the vehicle, but also combinations of the two concepts, or other variations, are possible. Common for all hybrid concepts is that there is some kind of energy management system, EMS, controlling the propulsion and energy distribution of the vehicle.
It is well known that for conventional ICEs the main part of all engine wear is caused during the first seconds after engine start up since the oil has drained away from the bearings, cylinder walls and other wear points in the engine. During normal ICE start up, some kind of lubrication system for the ICE circulates oil under pressure through the engine block, cylinder head etc. for lubrication of moving engine parts. But not only has the oil drained away when the engine has been turned off, the oil has also been cooled down, making it more viscous, which counteracts the lubrication of the engine during engine start up. The oil pressure builds up slowly, and during this time the main part of the engine wear is caused. After a few seconds the oil pressure reaches operational level and as the engine gets warmer the oil gets warmer, which lowers the viscosity of the oil.
By utilizing some kind of pre-lubrication system before engine start up, the internal friction can be lowered and the engine wear can be minimized, which will increase the engine lifetime.
Additionally, during the first engine revolutions, when the engine is drained of oil and the oil is cold, the engine will also cause more noise than during normal engine operation.
For Plug-in Hybrid Electrical Vehicles, PHEVs, Hybrid Electrical Vehicles, HEVs, or other vehicles with some kind of hybrid propulsion, with at least one EE and at least one ICE, this will also have another effect. For PHEVs or HEVs starting the vehicle might imply only starting the EE, hence the ICE will not be ignited automatically by turning the key. By not automatically starting the ICE, or by at least postponing the ignition, it is possible to save fuel and lower the vehicle exhaust emissions, as already stated; two of the biggest drivers for automotive industry during the last decades.
For newer PHEVs and HEVs, the driver generally has a lot of options regarding how the driver prefers the vehicle to function, regarding for example engine response and fuel consumption. If the ICE should be started when starting the vehicle might be up to the driver to decide by using different drive modes, where drive modes such as e.g., “eco”, “city”, “hybrid” or such might imply initially only starting the EE, thus enabling a more environmentally and low fuel consumption mode, and modes like e.g., “power”, “force”, “highway” or such might imply initially starting only the ICE, or both the ICE and EE, for better engine performance.
If the ICE is not ignited when starting the vehicle, the ICE might first be ignited during speed when the driver makes a torque demand where the EE can no longer supply sufficient power. For almost all hybrid vehicles today with both an EE and an ICE the ICE can deliver higher torque than the EE. Starting the ICE when the vehicle is already travelling at speed, the crankshaft of the ICE, and other moving parts, will initially revolve faster than if starting from standstill, which makes rapid lubrication of the moving parts of the ICE even more important.